1. Field of the Invention
The present invention relates to an accessory module for a stereo microscope.
2. Relevant Prior Art
A series of possibilities exists for varying the stereo angle between the two observation beam paths in a stereo microscope. Thus it is known from German Utility Model G 1,827,188 of the Applicant's employer to pivotably arrange two planar plates between the main objective and a device for changing the magnification. The two planar plates are pivotable around the optical axes of the stereoscopic observation beam paths, so that a variation of the stereo base is made possible by means of a suitable operating element. In this apparatus, on pivoting the planar plates, the observation beam paths no longer pass symmetrically through the main objective in intermediate positions; moreover, the plane which is defined by the two stereoscopic beam paths moves perpendicularly to the main objective. As a result, the observer's perspective changes when the stereo angle is varied. Furthermore, when the stereoscopic beam paths pass through edge regions of the main objective, a deteriorated image quality occurs because the optical correction is not optimal in these edge regions.
A further possibility for varying the stereo base is known from U.S. Pat. No. 4,838,671 (European Patent EP 242,321). A suitable prism, which consists of two plane-parallel plates including between them a defined angle, is fixedly arranged on a common rotor. Its axis of rotation is oriented perpendicular to the observation beam paths, or this axis lies in a plane which is spanned by the two observation beam paths. A total of three different stereo angles results, according to the pivoted position of the rotor of the prism, between the two observation beam paths, i.e. the possibility of varying the stereo angle is limited to three discrete stereo angles.